An electronic part called an autofocus camera module (AFM) is used in camera lens sections for mobile phones. The autofocus function of the camera for the mobile phone moves the lens in a fixed direction by spring force of the material used for the AFM, while moving the lens in a direction opposite to the spring force-acting direction by means of electromagnetic force generated by passing an electric current through a coil wound around the periphery. By such a mechanism, the camera lens is driven to exert the autofocus function (for example, Patent Documents 1 and 2).
Therefore, a copper alloy foil for use in the AFMs requires strength sufficient to withstand deformation of the material due to the electromagnetic force. If the strength is low, the material cannot withstand displacement due to the electromagnetic force, and permanent deformation (settling) will occur. If the settling occurs, the lens cannot move to a desired position and the autofocus function cannot be produced, when a constant current is passed.
For spring materials for AFMs, Cu—Ni—Sn based copper alloy foils having a foil thickness of 0.1 mm or less and tensile strength of 1100 MPa or more have been conventionally used. However, a recent demand for cost reduction has led to the use of titanium copper foils which have relatively lower raw material costs than the Cu—Ni—Sn based copper alloys, and the demand for the titanium copper foil is thus increasing.
Under such circumstances, various titanium coppers suitable as spring materials for the AFMs have been proposed. For example, Patent Document 3 has proposed a titanium copper foil wherein it comprises Ti of 1.5 to 5.0% by mass, the balance being copper and inevitable impurities, and 0.2% yield strength in a direction parallel to a rolling direction is at least 1100 MPa, and it satisfies a relationship: I(220)/I(311)≥15 where I(220) and I(331) represent integrated intensities for a plane (220) and a plane (331), respectively, as measured using an X-ray diffraction analysis in the rolling plane, in order to improve the 0.2% yield strength and settling resistance for the titanium copper foil. Further, Patent Document 4 has proposed a titanium copper foil wherein it comprises Ti of 1.5 to 5.0% by mass, the balance being copper and inevitable impurities, wherein 0.2% yield strength in a direction parallel to a rolling direction is 1100 MPa or more, and wherein arithmetic average roughness (Ra) in a direction perpendicular to the rolling direction is 0.1 μm or less, for the purpose of improving settling resistance.